Vinyl halide polymers, particularly polyvinyl chloride resins, are used in a variety of applications. These thermoplastic polymers can be fabricated into useful articles by extrusion, injection molding, compression molding and other thermoforming methods. To stabilize vinyl halide polymers during thermoforming methods, heat or thermal stabilizers and co-stabilizers are added to the resins. Examples of known stabilizers include organometallic stabilizers, mixed metallic stabilizers, and inorganic stabilizers. Metallic stabilizers include heavy metal, alkali metal and alkaline earth metal salts of fatty acids. The heavy metals include lead, cadmium, tin and zinc. Examples of mixed metallic stabilizers include fatty acid salts of zinc and calcium, zinc and barium, barium and cadmium, lead and barium, or two or more of other metals. Examples of inorganic stabilizers include lead carbonate, lead sulfate, and mixtures of tribasic lead sulfate and dibasic lead stearate. Examples of organic, non-metallic stabilizers or co-stabilizers include epoxidized soybean oil, tris nonylphenyl phosphite, beta diketones, and phenylindole.
Stabilization of polyvinyl chloride has also been addressed in cases where organic nitrogen-induced degradation becomes a problem such as in applications in which polyvinyl chloride is affixed to a urethane foam backing. The residual amine catalyst in the polyurethane is the degradation catalyst.
Among the references pertinent to this general area of technology are the following:
1. U.S. Pat. No. 5,034,443 to K. Bae et al. describes stabilizer compositions which are free-flowing powder compositions and which contain blends of sodium perchlorate hydrate and calcium silicate. This patent also describes a solution of sodium perchlorate in water with calcium silicate and a non-absorbing diluent powder, such as calcium carbonate, to provide a "free-flowing powder composition".
2. U.S. Pat. No. 4,861,816 to M. Kobayashi describes a solid stabilizer mixture of a barium salt of a carboxylic acid and a zinc salt of a carboxylic acid, each having a melting point of no lower than 250.degree. C., with a metal perchlorate and/or perchlorate ion type hydrotalcite compound.
3. U.S. Pat. No. 4,957,954 to S. Iizuka et al. describes a stabilizer comprising a 2,2,6,6-tetramethyl piperidinyl compound and an ammonium or metal perchlorate.
4. Japanese Patent Publication No. 61/272,258 describes heat stabilizers containing a predominant amount of organic tin compounds with lower amounts of hydrotalcites and still generally lower levels of barium perchlorate.
5. Japanese Patent Publication No. 04/50,250 describes solid powder stabilizers comprising Group IA metal salts of perchloric acid, hydrotalcite and/or zeolites, and organic powder.
6. Japanese Patent Publication No. 04/183,735 describes use of compositions comprising organic acid salt(s) of (1) sodium, potassium, magnesium, calcium, barium, and zinc and alkyltin compounds; (2) sulpholene compounds; and (3) .beta.-diketone compounds of a certain formula or their sodium, magnesium, calcium, barium or zinc salts.
Tadenuma and co-workers in U.S. Pat. No. 5,004,776 describe stabilized chlorine-containing resin compositions which contain a stabilizer consisting essentially of: (a) an overbased alkaline earth metal carboxylate or phenolate complex; (b) zeolite; (c) calcium hydroxide; and (d) a perchlorate-alcohol complex. This overall stabilizer would not be expected to be a clear, homogeneous liquid since components (b) and (c) are solids. While it is true that this patent shows the synthesis of liquid perchlorate-containing additives, (d), such a component is not taught for use with a solubilized metal perchlorate in a stabilizer composition which is a homogeneous, clear liquid, but is only taught for use with zeolite and calcium hydroxide as additional, necessary stabilizer additives. This patent also fails to show mixing of components (a) and (d) only in any form of premix.